X-ray imaging of vortex cores in confined magnetic structures

Fischer, Peter; Im, Mi‐Young; Kasai, S.; Yamada, K.; Ono, Teruo; Thiaville, A.

doi:10.1103/physrevb.83.212402

Cited by 31 publications

(28 citation statements)

References 31 publications

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“…Vortices have a winding number of n = + 1 and a polarity of p = ± 1, whereas antivortices have n = − 1 (refs 1-3). Magnetic vortices are characterized by an in-plane curling magnetization (chirality) and a nanometer-sized central region with an out-of-plane magnetization (polarity) [4][5][6] . The latter is defined by a clockwise (c = 1) or counter-clockwise (c = − 1) rotation of the in-plane magnetization.…”

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Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk

et al. 2012

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The magnetic vortex in nanopatterned elements is currently attracting enormous interest. A priori, one would assume that the formation of magnetic vortex states should exhibit a perfect symmetry, because the magnetic vortex has four degenerate states. Here we show the first direct observation of an asymmetric phenomenon in the formation process of vortex states in a permalloy nanodisk using high-resolution full-field magnetic transmission soft X-ray microscopy. micromagnetic simulations confirm that the intrinsic Dzyaloshinskii-moriya interaction, which arises from the spin-orbit coupling due to the lack of inversion symmetry near the disk surface, as well as surface-related extrinsic factors, is decisive for the asymmetric formation of vortex states.

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Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk

et al. 2012

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“…A first approach consists in directly mapping the sample magnetization, which implies sending and collecting back test particles whose interaction with matter has a magnetization-dependent term. This approach provides the highest spatial resolution to date, down to the atomic scale for spin-polarized scanning tunnelling microscopy 2 and about 10 nm in transmission X-ray microscopy 3 . However, these techniques require highly complex experimental apparatus and a dedicated sample preparation so that the particles can reach and escape from the tested region without perturbations.…”

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Stray-field imaging of magnetic vortices with a single diamond spin

et al. 2013

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Despite decades of advances in magnetic imaging, obtaining direct, quantitative information with nanometre scale spatial resolution remains an outstanding challenge. Recently, a technique has emerged that employs a single nitrogen-vacancy defect in diamond as an atomicsize magnetometer, which promises significant advances. However, the effectiveness of the technique when applied to magnetic nanostructures remains to be demonstrated. Here we use a scanning nitrogen-vacancy magnetometer to image a magnetic vortex, which is one of the most iconic objects of nanomagnetism, owing to the small size (B10 nm) of the vortex core. We report three-dimensional, vectorial and quantitative measurements of the stray magnetic field emitted by a vortex in a ferromagnetic square dot, including the detection of the vortex core. We find excellent agreement with micromagnetic simulations, both for regular vortex structures and for higher-order magnetization states. These experiments establish scanning nitrogen-vacancy magnetometry as a practical and unique tool for fundamental studies in nanomagnetism.

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“…Thus, simulations and experiments with larger films and, consequently, longer relaxation times, would be useful. For experimental investigation, time-resolved x-ray imaging techniques should have good enough spatial and temporal resolutions (25-30 nm and 70-100 ps, respectively) [39][40][41] to observe the defects and their dynamics. Even though these resolutions are still limited when compared to our simulations, the longer relaxation times and larger interdefect separations expected during the later stages of the relaxation process in larger films (e.g., with linear sizes in the range of tens of microns) should make it possible to experimentally observe the approximate time evolution of the vortex-antivortex number densities.…”

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Coarsening dynamics of topological defects in thin permalloy films

Rissanen

Laurson

2016

Phys. Rev. B

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We study the dynamics of topological defects in the magnetic texture of rectangular permalloy thin-film elements during relaxation from random magnetization initial states. Our full micromagnetic simulations reveal complex defect dynamics during relaxation towards the stable Landau closure domain pattern, manifested as temporal power-law decay, with a system-size-dependent cutoff time, of various quantities. These include the energy density of the system and the number densities of the different kinds of topological defects present in the system. The related power-law exponents assume nontrivial values and are found to be different for the different defect types. The exponents are robust against a moderate increase in the Gilbert damping constant and introduction of quenched structural disorder. We discuss details of the processes allowed by conservation of the winding number of the defects, underlying their complex coarsening dynamics.

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X-ray imaging of vortex cores in confined magnetic structures

Cited by 31 publications

References 31 publications

Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk

Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk

Stray-field imaging of magnetic vortices with a single diamond spin

Coarsening dynamics of topological defects in thin permalloy films

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